The invention relates to a connection of an electrical cable, especially one constructed of several aluminum wires or flexible leads and insulated aluminum cables, with a connection piece made of copper, copper alloy and/or brass or similar metal, for example with a battery clamp, a cable lug, a connection adapter, a plug element, a cable piece or the like, for the electrical system of a motor vehicle. The insulation of the aluminum cable ends before or at a distance from the contact point with the connection piece, and a support sleeve is provided, which encloses at least a region adjacent to the end face of the stripped (bared) part of the aluminum cable and is crimped and/or shrunk on the end of the aluminum cable, so that the wires of the aluminum cable are crimped together at least in the area of the end face.
The invention further relates to a process for connecting an electrical aluminum cable with a connection piece made of copper, copper alloy and/or brass or similar metal, for example a battery clamp, cable lug, connection adapter, plug element, cable or the like, for the electrical system of a motor vehicle. Here, the end face of the aluminum cable is brought into connection and electrical contact with the end face of the connection piece, and for this purpose the aluminum cable is bared (stripped of insulation) on the connection end. A support sleeve is crimped or shrunk on the stripped place, and the wires or flexible leads of the aluminum cable are thereby crimped together.
The idea is already known of replacing current-conducting leads of copper or copper alloys, especially energy leads, having a relatively large cross section in motor vehicles, with ones of aluminum, because aluminum even leads to a lower weight if the lead cross sections must be enlarged due to the somewhat lesser conductivity of aluminum in comparison with copper.
In this connection, experiments were conducted, and in U.S. Pat. No. 2,806,215, it was proposed to join the parts to be connected, i.e., an aluminum cable and a corresponding connection piece, by means of ferrules and clamps so as to conduct electricity. There, the problem nonetheless exists that, on the surface of aluminum under the influence of air oxygen, a thin oxide layer arises, whose thickness increases with time and which does not conduct electricity. The electrically conducting connection of an aluminum cable with a connection piece of another metal therefore requires the elimination or the penetration of such an oxide layer, and the prevention of a renewed formation of such an oxide layer.
Furthermore, with the connection of an aluminum cable made of individual wires or flexible leads with a connection piece, there results the necessity, for diminishing electrical resistance, of undertaking a clamp connection with high compressive force. This leads to deformations at the crimping site of the cross sections of the individual aluminum wires, so that these are weakened from the outset at the juncture point and can break under the dynamic stress in a motor vehicle in the course of time. Especially high dynamic stresses arise here in the area of the driving motor, the dynamo and even the battery.
On the other side, it is not possible to make the connection piece itself likewise of aluminum, because in the area of batteries or accumulators acid vapors cannot be entirely ruled out, which attack aluminum to a considerably greater extent than copper, copper alloys or brass, and because connections to units joined with a combustion motor, such as dynamos, are exposed to such a high dynamic stress that, in the course of time, the less stable aluminum material breaks or the connection juncture is destroyed.
Aluminum is also subject to a greater danger of corrosion than copper, which has a relatively good corrosion resistance, because aluminum is relatively electronegative. For this reason, aluminum has the tendency to convert to the more stable oxide form, from which is was created under the application of energy.
If metals of varying base character are conductively connected with one another, there exists the danger of a contact corrosion. Here, due to their electropositive potential, copper materials are less degradable than aluminum, but can also exert a degrading action on this metal in a connection with it. Since aluminum is the more electronegative metal in comparison with copper, it can also occur in a contact connection with high currents and longer stress times, chiefly in a humid, salt-containing climate, that the more electronegative metal, i.e., the aluminum, acts as the xe2x80x9csacrificial anodexe2x80x9d and deteriorates. Thus, with time, a loss of material occurs on the contact surface, which has a negative effect on the contact resistance and stability.
Even with the use of an aluminum ferrule surrounding the stripped aluminum cable, and welding it with a connection piece of copper, according to FIG. 8 of U.S. Pat. No. 2,806,215, there exists the problem, within the aluminum ferrule, between the front ends of the aluminum wire and the connection piece made of copper, that a seam or a space remains and, in the course of time, the previously mentioned contact corrosion arises.
For this reason, there exists the object of creating a connection of the type mentioned at the beginning, which has a high degree of stability in relation to the dynamic stresses and a good conductivity, and which, on the one hand, eliminates an oxide layer or corrosion on the aluminum in the area of the juncture by the connection operation itself and/or, on the other hand, prevents an oxide layer in this area of mutual contacting of the different metals.
For accomplishing this objective, the initially mentioned connection of an electrical aluminum cable with a connection piece of another metal is wherein the connection piece is welded with the end face of the aluminum cable formed by the individual wires.
The connection is thus chiefly characterized by an additional support sleeve on the aluminum cable, which sufficiently stabilizes the individual wires or flexible leads by crimping them together and draws them closer to one another, in order to yield a metal surface on the end face of the cable, which is then at the same time the connection point or the place of welding with the connection piece. It is thereby possible to free this face of oxide, to the extent that it may have formed there, and then to butt weld this face with the connection piece, so that in the future as well no oxide can arise at this spot. As is well known, aluminum can be easily fused or welded with copper and thus, in the connection of the invention, even form a mutual alloy. Experiments have shown that the resistance to wear of such a connection can be higher than that of the aluminum cable and/or the connection piece themselves.
Since the individual wires of the aluminum cable themselves can be welded with the connection piece, and thereby also with themselves, there results a sub-metallic connection between the aluminum cable and its individual wires and the connection piece consisting of copper or a copper alloy, which can extend over the entire end face cross-sectional area. This sub-metallic connection layer, according to experiments, can be about 2 mm thick, so that an air or moisture access to this connection site is ruled out.
It is especially beneficial if the support sleeve reaches beyond the transition between the stripped region of the aluminum cable and the insulation, including a part of the insulation. The support sleeve thus expediently maintains a longer axial length than the stripped area of the aluminum cable, so that a good stiffening is attained in the area of the connection point up to under the insulation, which leads to an even distribution of the compressive forces in the connection area, without subjecting the individual aluminum wires too strongly to stress and to deformation. Consequently, such a connection point is also a match for shearing forces and dynamic stresses, as they can also occur in motor vehicles in reference to units connected with the motor. At the same time, a good sealing of the aluminum cable and the connection can be obtained.
Here, it is expedient if the one end of the supporting sleeve is flush with the end face of the stripped region of the aluminum cable. The support sleeve thereby then enlarges the connection point radially and is itself also available for welding with an appropriately proportioned connection piece or counterpart to the extent that the support sleeve crimping the end of the aluminum cable together is a metal sleeve, especially an aluminum sleeve. Above all, an aluminum sleeve has in this connection the advantage that it behaves, with reference to heat expansion, electrical conductivity and weldability, like the aluminum cable itself, and is thus to a certain extent an enhancement of the aluminum cable at the connection point.
It is especially beneficial if the aluminum cable and the shrunken on or crimped on support sleeve and the connection piece basically have a circular cross section, in particular of the same size. The welding point can then extend over the entire cross section of the connection and thereby at the same time over the entire cross section of the connection piece, on the one hand, and the unit formed by the aluminum cable and support sleeve, on the other hand. Correspondingly beneficial resistance values for the electric current can be attained on this large-area connection.
For the best possible distribution of compressive forces on the individual wires or flexible leads of the aluminum cable, it is beneficial if the support sleeve for crimping or pre-crimping the aluminum cable has in its interior at least two segments of different inside cross section or inside diameter. The segment with the larger inside diameter grips around the end of the insulation of the aluminum cable, and the segment of smaller inside diameter grips around the stripped area of the aluminum cable. Here, the difference between the inside diameters of the support sleeve corresponds approximately to double the thickness of the insulation of the aluminum cable.
With this configuration of the support cable, it is thus possible to take into account the cross sectional difference between the insulated and the non-insulated part of the aluminum cable, so that the support sleeve has a largely constant circumference before and even after the crimping on its exterior. The crimping means need not take into consideration any differences in cross section, although these are present in the interior of the support sleeve on the aluminum cable. Since the end of the crimping facing away from the connection point can be arranged in an insulated region of the aluminum cable, the individual wires of the cable are protected against excessively strong mechanical deformations due to the crimping operation, and consequently retain their stability.
It was already mentioned that the connection can be completed by butt welding. Here it is especially beneficial if the end of the aluminum cable provided with the support sleeve is joined with the connection piece by friction welding. Friction welding is known per se. In many cases this is brought about by bringing one of the pieces into rotation before the connection, then moving it against the other part, whereby frictional heat arises, which is high enough for welding the parts, so that they are connected firmly with each other after braking the rotation. Above all, in joining an aluminum cable with a connection piece, an oxide layer possibly arising at the connection point or end face of the aluminum cable can at the same time be automatically eliminated, because such a layer is penetrated and removed by the mechanical friction. Consequently, an electrical connection of an aluminum cable with a connection piece by friction welding is to be viewed as especially advantageous and beneficial, since relatively low energies are necessary for this type of welding, for example in comparison with an even conceivable flash butt welding.
The process, already mentioned at the beginning for accomplishing the objective, is wherein the individual wires or flexible leads of the aluminum cable are butt welded together with the support sleeve having the connection piece. Instead of applying expensive clamp connections, in which a mechanical clamping and joining of the two parts to be connected is carried out and which possibly must subsequently once again be encapsulated with plastic, the two parts of different materials are thus welded to each other. Here, the soft and flexible end face of the aluminum cable is first mechanically fastened by a support sleeve, in order to withstand the stresses of welding and to make this end face of the aluminum cable suitable for direct welding with a connection piece. There results here a practically closed metal surface formed from the individual wires or flexible leads of the aluminum cable.
In this connection, it is further expedient to proceed in that the support sleeve is arranged with one end flush to the end face of the aluminum cable. That is, one end of the support sleeve is relied upon and used to enlarge the end face of the aluminum cable and thereby of the connection point. At the same time, it is assured that on the face, the individual wires or flexible leads of the aluminum cable are also in fact arranged all crimped together and fastened with each other, on the one hand, and are nevertheless accessible for welding. These wires can furthermore be flush with one another and form a flat face or cross section surface.
An especially favorable method can consist in that the aluminum cable provided with the support sleeve is joined with the connection piece by friction welding. In comparison with an electrically supported butt welding process, it is advantageous that substantially less energy is required for this. Nevertheless, the friction welding process permits a welding of the materials, namely aluminum on the one hand and copper or a copper alloy or similar metal on the other hand, with the formation of intermetallic phases. That is, the oxide layer on the aluminum is destroyed, and the possibility of corrosion at the connection point is eliminated. Since the aluminum cable is crimped with the support sleeve before or at the latest simultaneously with the welding process, there arises a type of solid cylinder on whose end face or head surface the welding can take place. The crimping of the individual wires of the aluminum cable thus need only be good enough to withstand the stresses of the welding process. At the same time, such a friction welding process goes along with a slight loss of metal at the joining and welding point, which stands out in the form of a bulge around the seam, which at the same time enlarges the connection point and thereby strengthens the connection itself.
It is especially beneficial if the connection piece to be connected or butt welded with the aluminum cable is rotated and crimped while rotating against the end face of the aluminum cable, and is thereby fused or welded by the frictional heat arising after braking the rotation. Indeed, the friction and the frictional heat can also be brought about by other reciprocal relative movements. However, rotation has the great advantage that the parts to be connected can already occupy their final position in the transverse direction, and almost any desired number of rotations can be generated on the rotating part, in order to obtain enough frictional heat for the welding. At the same time, an oxide layer thus possibly situated on the aluminum side can be especially effectively penetrated and eliminated.
The wires or flexible leads of the aluminum cable can be crimped together before and/or during the welding process at least in the area of the end face connection point, which can be especially simply carried out with the above-mentioned support sleeve. Here, the support sleeve can be crimped flat on its exterior, especially into a polyhedron, for example into a hexagon. There thereby results, in addition, with the later assembly the possibility for a tool engagement, for example for engagement by a monkey wrench. Moreover, such a polyhedral shape on the exterior of the support sleeve can be advantageous in connection with the transfer and assembly of the cable with its connection piece.
The connection piece can either be a cylinder of copper or a copper alloy, for example brass, which for its part is connected with a corresponding connector or a cable clamp or a battery clamp or the like, or is already connected with it at the outset in one piece. Such a cylinder can be especially well set into rotation and be connected by friction welding with the appropriately prepared aluminum cable.
It is, however, also possible for a cable piece having wires made of copper, a copper alloy and/or brass, serving as a connection piece, to be crimped on its exterior with a support sleeve, especially of copper, copper alloy or brass or similar metal and butt welded with the face of the aluminum cable. Situations are namely conceivable where indeed cables essentially made of aluminum are used which, however, must nonetheless still be joined with a piece of a copper cable, particularly if high dynamic stresses can arise in the area of the connection point, or in the further course of such an electrical lead a material pairing requires copper or a copper alloy. In such a case, the connection piece to be connected with the aluminum cable can for its part be a cable piece made of copper wires or the like, which likewise is stabilized by means of a support sleeve. A friction welding process is thus made possible in particular by rotation, preferably of the copper element, whereby then the cable itself and the support sleeves are joined with each other and welded.
A device for implementing the process for connecting an aluminum cable with a connection piece of another metal can above all consist in that an openable jig is provided for the aluminum cable provided with the support sleeve, and a separable mounting arranged in alignment therewith is provided for the connection piece. The mounting has a rotary drive or is couplable with one, and the jug and the mounting are movable or displaceable relative to each other in the direction of longitudinal extension of the aluminum cable or of the connection piece aligned with it at least upon mutual contact. Here it is especially beneficial if the rotating mounting is displaceable. This displaceability then includes the necessary compressive force on the connection point, which is exerted during welding. Moreover, the openable jig for the end of the aluminum cable can at the same time be relied on for crimping the support sleeve provided there.
Chiefly in the combination of single or several of the above-described features and measures, there results a connection of an aluminum cable serving for electrical transmission, in which it is not possible or necessary to weld directly on the individual wires or flexible leads, but instead a support sleeve is provided made expediently of aluminum, thus the same material, whereby the wires and flexible leads can be pre-sealed. Consequently, a type of solid cylinder is formed, which simultaneously also serves as a seal over the insulation, because it can extend up to over this insulation. This seal has passed a water tightness test with a meter water column. The connection point itself has a high electrical conductivity, because an oxide layer possibly previously present on the aluminum side, and under certain circumstances even present on the copper side, can be eliminated with a relative reciprocal rotation, so that the two different metals reach an intermetallic phase and are fused and welded to each other.